Generally, there are four classes of pollutant that are legislated against by inter-governmental organisations throughout the world: carbon monoxide (CO), unburned hydrocarbons (HCs), oxides of nitrogen (NOx) and particulate matter (PM). As emissions standards for permissible emission of pollutants in exhaust gases from vehicular engines become progressively tightened, there is a need to provide improved catalysts that are able to meet these standards and which are cost-effective.
For compression ignition engines, such as diesel engines, an oxidation catalyst (known as a diesel oxidation catalyst (DOC)) is typically used to treat the exhaust gas produced by such engines. Diesel oxidation catalysts generally catalyse the oxidation of (1) carbon monoxide (CO) to carbon dioxide (CO2), and (2) HCs to carbon dioxide (CO2) and water (H2O). Exhaust gas temperatures for compression ignition engines, such as diesel engines particularly for light-duty diesel vehicles, are relatively low (e.g. about 400° C.) and so one challenge is to develop durable catalyst formulations with low “light-off” temperatures.
The activity of oxidation catalysts, such as DOCs, is often measured in terms of its “light-off” temperature, which is the temperature at which the catalyst starts to perform a particular catalytic reaction or performs that reaction to a certain level. Normally, “light-off” temperatures are given in terms of a specific level of conversion of a reactant, such as conversion of carbon monoxide. Thus, a T50 temperature is often quoted as a “light-off” temperature because it represents the lowest temperature at which a catalyst catalyses the conversion of a reactant at 50% efficiency.
EP 2000639 describes a method for increasing the temperature of an exhaust gas from an internal combustion engine, particularly a diesel engine. EP 2000639 is concerned with increasing the temperature of an exhaust gas because it can assist the regeneration of a particulate filter placed downstream from the catalyst. The method described in EP 2000639 involves introducing hydrocarbon (HC) in an amount of from 1,000 to 40,000 ppm by volume, as converted to methane, to the exhaust gas upstream of a catalyst. The catalyst is obtained by supporting a catalytically active component (A) consisting of (a) platinum, (b) an oxide of at least one metal selected from the group consisting of magnesium, an alkaline earth metal and an alkali metal, and (c) at least one member selected from the group of palladium and rhodium, on a refractory inorganic oxide powder (B), and supporting the inorganic oxide on a refractory three-dimensional structure body.